The present invention relates to the field of hermetically sealed connector feedthrough modules which are subjected to pressure and temperature extremes, and is more particularly, an improved fiber optic feedthrough module configuration suited for use in such adverse environmental conditions. The present invention also delineates the structure of and the method of making a hermetically sealed fiber optic feedthrough module which will withstand adverse pressure and temperature extremes.
Connector or bulkhead penetration fiber optic feedthrough modules have particular application in systems such as in nuclear power facilities, rocket engines, and other types of explosive environments where durability and rugged performance requirements are critical.
In the past, electrical connector penetrant structures have been developed for passing one or a plurality of electrical conductors in a single module through a bulkhead structure while maintaining a pressure seal around the electrical conductors. Typical structures are shown in U.S. Pat. Nos. 3,601,526 and 3,680,208.
Fiber optic bulkhead penetrant feedthroughs have been developed which employ metallic film optical fiber protection and a compression method of assembly to hermetically seal the plurality of fibers within the feedthrough housing. Examples are U.S. Pat. Nos. 4,296,996, 4,593,970 and 4,891,640. Bulkhead feedthroughs typically accommodate pressure differentials of 10.sup.-6 to 10.sup.-8 cc/sec. helium leak rate. The invention described herein can provide up to 10.sup.-11 cc/sec. helium leak rate. Other feedthroughs are limited in component materials and structural limitations which can be accommodated such as U.S. Pat. Nos. 4,859,021, 4,822,130 and 4,682,846. The present invention can effectively bond glass, ceramic, metal or composite materials to optical fiber.
The use of electrical conductors has certain disadvantages in some applications such as an electromagnetic interaction between the conductors and/or the system around them. This interaction is either an inducted electrical current into a sensor or control line by an ambient changing magnetic field or the effect on the system of a changing magnetic field created by current flow in the electrical conductor.
With the advent of fiber optics, such electromagnetic disadvantages are avoided by the elimination of current flow down the conductor and replacing this current flow with optical pulses traveling along an optical waveguide. However, fiber optics also have unique disadvantages such as the fragility of the optical fiber elements to shear forces or micro-bending losses.
Accordingly, the primary object of the present invention is to provide a fiber optic feedthrough module which is capable of utilization in extremely hostile environmental conditions, to withstand pressures in excess of 30,000 psi and/or a temperature range of from 200.degree. C. to higher than +200.degree. C., or in nuclear environments to withstand a transient dose of 10.sup.12 rads or a total dose of 10.sup.9 rads, or to withstand high vibration levels of 40 G's with random vibration from 10 Hertz to 2000 Hertz, or to withstand high shock and acceleration levels.
The present invention overcomes the shortfall of previous fiber optic feedthrough modules in that there is no longitudinal force caused by a swaging operation to put the optical fiber in a possible compression mode which would cause micro-bending and excess signal losses in the optical fiber.
The present invention, a fiber optic feedthrough module, being capable of transmitting optical signal(s), can be employed as a component in applications such as suitable control circuits, and operatively associated with instrumentation where signal penetration through a bulkhead is required. The module may be sized to fit a particular application regarding the number of fibers contained in the feedthrough module in relation to the housing diameter or the length dimension in relation to the style of feedthrough module housing, and can be used with conventional hermetic bulkhead mounting and sealing hardware. The connector-style housing may utilize any standard electrical or fiber optic connector coupling mechanism.
Besides use in the Space Shuttle main engine type applications, said fiber optic feedthrough modules have practical application in nuclear power plants, in explosive environments, in pressure extremes (exceeding standard atmospheric pressure or in vacuum), in military and aerospace equipment exposed to high radiation levels, and in underwater applications that require a hermetically sealed feedthrough module.